Generally, a rotary compressor has a motor-driven compression member provided within a closed casing. This compression member comprises: a cylinder which has a cylinder chamber, and a suction port and a discharge port both opened to the cylinder chamber; a roller which is insertedly fitted to an eccentric shaft of a drive shaft extending from the motor and which revolves in the cylinder chamber along with rotation of the drive shaft; and a blade which is supported at an intermediate portion between the suction port and discharge port of the cylinder so as to be free to advance and retreat radially. The blade is so arranged that part of high-pressure gas discharged from the discharge port acts on its back face as back pressure, which back pressure in turn causes the tip of the blade to be always kept in contact with the outer peripheral surface of the roller. As a result, the interior of the cylinder chamber is partitioned into a low-pressure chamber communicating with the suction port and a high-pressure chamber communicating with the discharge port.
However, when the blade is supported to the cylinder so as to be free to advance and retreat, and has back pressure given on its back face side so that the tip of the blade is always kept in contact with the outer peripheral surface of the roller as described above, the contact portion between the blade and the outer peripheral surface of the roller is poorly fed with lubricating oil so as to be brought into metallic contact, during relative rotation of the roller and the blade. The result would be greater friction loss due to sliding resistance and therefore greater power loss, to a disadvantage. Further, high-pressure gas compressed in the high-pressure chamber may leak through the contact portion between the tip side of the blade and the roller into the low-pressure chamber. This would cause another problem that compression efficiency deteriorates.
Thus, the present inventor has before proposed a rotary compressor which can solve the above problems (Japanese Patent Application No. HEI 4-252750). Although this patent application has not been laid open yet, nor is it the prior art of the present invention, yet it is here described for an easier understanding of the present invention. The rotary compressor, as shown in FIG. 8, comprises a cylinder A having a cylinder chamber A1, and a roller C fitted to an eccentric shaft B1 of a drive shaft B and internally provided in the cylinder chamber A1. In the rotary compressor, a blade D is coupled with an outer peripheral portion of the roller C so as to protrude radially outward, while a retainer hole A5 of circular shape in cross section having an opening A4 opened to the cylinder chamber A1 is formed at an intermediate portion between a suction port A2 and a discharge port A3 both provided in the cylinder A. In this retainer hole A5 is provided a swinging bushing E which has a receptive groove E1 for receiving the protruding tip side of the blade D in such a way that the tip side of blade D is free to advance and retreat, and which is swingably retained to the cylinder A. In this arrangement, the protruding tip side of the blade D is inserted into the receptive groove E1 of the bushing E so as to be free to advance and retreat, whereby the interior of the cylinder chamber A1 is partitioned into a low-pressure chamber Y communicating with the suction port A2 and a high-pressure chamber X communicating with the discharge port A3. Besides, the blade D is inserted into the bushing E, whereby the roller C is non self-rotary type and operates along the inner peripheral surface of the cylinder chamber A1. It is noted that, in FIG. 8, reference character F denotes a valve plate disposed on the outer side of the discharge port A3 and G denotes a receptive plate of the valve plate F.
With the roller C in operation within the cylinder chamber A1 by the drive of the drive shaft B, the blade D coupled with the outer peripheral portion of the roller C is moved to advance and retreat with respect to the receptive groove E1 in accompaniment by the swing of the bushing E. By this operation, the interior of the cylinder chamber A1 is partitioned into the high-pressure chamber X and the low-pressure chamber Y. Gas fluid is sucked through the suction port A2 into the low-pressure chamber Y, while gas fluid compressed in the high-pressure chamber X is discharged through the discharge port A3 to the outside.
As described above, in the so-called swinging type blade in which the blade D is provided on the outer peripheral surface of the roller C so as to protrude radially outward and the protruding tip side of the blade D is inserted into the receptive groove E1 of the bushing E so as to be free to advance and retreat, the blade D and the roller C will not be moved relative to each other and the blade D will not be brought into contact with the outer peripheral surface of the roller C, either, unlike the conventional counterpart in which the protruding tip of the blade D is always kept in contact with the outer peripheral surface of the roller C. As a result, friction loss due to the contact between the roller C and the blade D can be suppressed so that power loss can be reduced. Yet, high-pressure gas in the high-pressure chamber X can be prevented from leaking through the contact surface between the blade D and the roller C into the low-pressure chamber Y, so that compressive efficiency can be improved.
However, according to the above-described arrangement, with the roller C in operation within the cylinder chamber A1, the tip side of the blade D protrusively provided on the outer peripheral surface of the roller C moves to advance and retreat within the receptive groove E1 of the bushing E, while the bushing E swingingly moves after the movement of the roller C within the retainer hole A5. As a result, when the roller C is operated, for example, clockwise in the figure, tensile stress in the direction of arrow Z in FIG. 8 concentrates on the low-pressure chamber Y side in the joint portion of the blade D to the roller C, while compressive stress concentrates on the high-pressure chamber X side in the joint portion of the blade D to the roller C. Due to this fact, the blade D has been easily fracture-damaged at the joint portion causing corresponding problems.